Synthesis and characterization of a new heavy-metal-selective inorganic ion exchanger

This study covers the methods and techniques used in the development of an inexpensive, inorganic ion exchange material composed of iron oxides. The synthesized sorbent (SISORB) has shown considerable removal capacity for environmentally significant solutes including heavy metals such as Pb+2, Cu 2, Zn2+, Ni2+, Cd2+ and the oxyanion, arsenate. In addition SISORB is mechanically stable, durable and easily regenerated making the sorbent reusable.; The process developed transforms precipitated iron hydroxides (PIHs) into a form amenable for use in both batch and fixed-bed configurations. By fusing dried PIHs at approximately 2000°C a clinker (mass of incombustible material) is formed. The clinker then crushed to a desirable size appropriate for a chosen reactor configuration. The synthesized sorbent can be altered from an anion-exchanger (SISORB I) to the cation-exchanger form, SISORB II, by the addition of a key component, synthesized akermanite, prior to the fusion process. Synthesized akermanite, like the natural mineral akermanite, is composed of oxides of calcium, magnesium and silica. Synthesized akermanite has the ability of maintaining a high pH over an extended period of time when water is passed over it. The chemistry is such that through the dissolution of akermanite, each (1) mole of akermanite will produce six (6) moles of hydroxyl ions. At the elevated pH, due to the hydroxyl ions produced, tests preformed show sorption kinetics to be faster than precipitation kinetics. When akermanite is combined with PIH it enables the selective ion exchange of SISORB II to take place over a wide pH range.; SISORB is selective towards target anion and cations (SISORB I - H2ASO4- > SO4 -2, SISORB II - Pb+2 > Cu2 > Zn 2+ > Ni2+ > Cd2+) at trace concentrations (ppb to ppm). Common ions found in surface and ground water, such as the anions nitrate and chloride and cations such as sodium and calcium, occur at concentrations greater than 100 times that of the target ions. Even with this competitive difference in concentration, tests show that target anions and cations are selectively removed by sorption.